1. Field of the Invention:
This invention relates to an improved fluorine type permeable polymer membrane suitable for desiccation of gases used in the production of semiconductor components such as silicon wafers, gases used in the production of semiconductor devices, gases used in the production of new articles such as fine ceramics, solar cells, and optical fibers and for desiccation of source gases, carrier gases, and ambient gases used in the chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods applied to the formation of ceramic or metallic thin-films on the surface of such substrates as optical components, precision machine components, general machine components, and heat ray-reflecting glass parts, a method for the production of the permeable membrane, a method for the desiccation of the various gases mentioned above, and an apparatus for the formation of a film by the use of the aforementioned permeable polymer membrane.
2. Description of the Prior Art:
It is those semiconductor devices called LSI and VLSI that lead the remarkable growth now taking place in the field of electronics. In the process for the production of their materials and the production of these devices, rare gases such as argon and helium, corrosive gases such as hydrogen chloride and chlorine, and special gases such as silane, arsine, and borane gas are used in addition to such general-purpose gases as nitrogen. Further in the process for the production of semiconductor devices, high integration (super-miniaturization) is advancing rapidly.
The lines forming miniature patterns have been gradually losing width and, as a result, the microfine dust particles which have not posed any noticeable problem have been manifesting an increasingly conspicuous influence on the yield of products in proportion to the growing degree of integration of LSI's from the present prevalent level of 256 K bits to 1 megabit and further to 4 megabits.
The gases used in the production of semiconductors mentioned above, specifically the gases used for silicon wafers as substrates of LSI's and for the operations of epitaxial growth, doping, etching, and cleaning in the processes for production of semiconductor devices have reached the point where they are required to possess purity of the order of 4 to 5 time or higher and, in addition thereto, to possess dryness of not more than 1 ppm of water content and enjoy perfect freedom from floating dust particles.
The water present in such a gas induces various hindrances as cited below. The water content, therefore, must be controlled strictly.
(1) The water causes corrosion of such metallic components as pipes, valves, and flowmeters used in the production process of semiconductors and consequent formation of fine metal impurities and fine particles (for example, such corrosive gases as HCl gas). PA0 (2) The water in the furnace for the production of semiconductors is decomposed into H.sub.2 and O.sub.2 and this O.sub.2 particularly gives rise to unexpected oxide impurities. PA0 (3) The gas itself and the entrained water are chemically combined to give rise to by-product impurities. PA0 (4) The surface of the susceptor used in the furnace is damaged to expose graphite.
The high desiccation of a gas mentioned above is important when metallic or ceramic coatings are formed on the surface of such substrates as components in optical devices and components of precision machines. The purity of a gas used in a CVD or PVD method has a serious effect on the construction and physical properties of the coating to be produced. The properties possessed by the produced coating improve in proportion as the purity of the gas is heightened.
At present, the method of adsorption by the use of a molecular sieve is partly adopted for the desiccation of gases to be used in the process for the production of semiconductor devices. The molecular sieve is a desiccant second in adsorbing ability to phosphorus pentoxide and rather readily desiccates an ordinary gas to below 1 ppm of water content.
This particular desiccant has found extensive utility because it has an advantage that, as a physical desiccant, it refrains from inducing such hindrances as deliquescence and swelling. It has a disadvantage, however, that its thermal regeneration necessitates an elevated temperature of 200.degree. to 400.degree. C. and its repeated use after the thermal regeneration entails occurrence of floating dust particles.
Further, the molecular sieve, on exposure to an acid gas such as hydrochloric acid gas, is disintegrated.
Although the molecular sieve is available in its acidproof grade, the formation of floating dust particles must be prevented. Thus, the molecular sieve inevitably necessitates attachment of a dust filter. In this case, the molecular sieve is no longer regenerable.
As means of desiccating gases, methods which resort to use of polymer membranes are disclosed in U.S. Pat. No. 3,735,558 and the specification of Japanese Patent Application Laid-open Print No. 60,563/1978, for example. Unlike the method of adsorption by the use of the molecular sieve, these methods of permeation through membranes have an advantage that their membranes can be used continuously for a long time without requiring any regeneration.
The former method utilizes a polymer particularly possessing a fluorine type sulfonate group and, therefore, is usable even with a corrosive gas. Neither of the methods, however, are capable of producing a gas having a water content of not more than 1 ppm and fitting a process of producing semiconductors.
The method of adsorption by the use of a disposable grade molecular sieve is not practicable because of a high running cost. Under these circumstances, the development of a method capable of easily producing a gas highly desiccated to not more than 1 ppm of water content at a low running cost without generation of floating dust particles is highly expected by the market.